Magnetic bearings are designed to provide a freely rotatable support to a rotating load without contacting the load, by utilizing the magnetic forces of attraction or repulsion. Such bearings feature low coefficient of friction, low vibration and low operating noise. Because they are applicable to equipment involving ultra highspeed rotations or vacuum systems, magnetic bearings are used in such critical applications as reaction wheels of satellite gyroscopes and in vacuum pumps for expelling gases from vacuum containers.
FIG. 17 is a perspective view showing a part of the construction of a conventional type of magnetic bearings. The numeral 1 refers to a freely rotatable shaft, 2 is a cylindrical rotor which is fixed to a part of the outer periphery of the shaft, and is composed of layers of soft iron. M.sub.1 -M.sub.4 refer to four electromagnets facing and surrounding the shaft, and disposed on the outer periphery of the rotor 2 with an airgap therebetween. The magnets M.sub.1 and M.sub.2 which are disposed along the x-axis face each other, and the magnets M3 and M4 which are disposed along the y-axis, orthognal to the x-axis, face each other. These four magnets are firmly fixed to the inner section of the stator. S.sub.1 -S.sub.4 are displacement sensors which are disposed on the outer periphery of the shaft 1 with an airgap, to sense the radial displacement of the shaft 1 and the rotor 2. They are disposed in the same relative spatial relationship as the electromagnets M.sub.1 -M.sub.4, and are fixed to the inner surface of the stator.
Such a magnetic bearing operates in the following way. A magnetizing current is passed through the coils C.sub.1 and C.sub.2, for energizing the corresponding electromagnets M.sub.1 and M.sub.2, the rotor 2 becomes aligned with the positive and negative poles along the x-axis; when a magnetizing current is passed through the coils C.sub.3 and C.sub.4, for energizing the electromagnets M.sub.3 and M.sub.4, the rotor 2 becomes aligned with the positive and negative poles on the y-axis, the combined effect produces leviation of the rotor 2 in an equilibrium balancing position between the two sets of magnetic forces. Although not shown in this figure, another magnetic bearing is arranged at the opposite end to support the shaft 1 in the horizontal direction, and a magnetic bearing is placed in the mid-portion of the shaft 1 in the thrust direction. Therefore a total of five sets of magnetic forces provide support to the shaft 1 so as to permit the shaft 1 to rotate freely without contacting any of the support sections.
Because of the design concept that a number of electromagnets M1 to M4 are fixed firmly on the inner periphery of the stator in the conventional types of magnetic bearings, the structure became complex and the overall apparatus incorporting such a conventional magnetic bearing could not be made compact.